A frame of this class has been known from the Applicant's patent No. EP-A-0 493 319. This is especially suitable for the installation of plumbing units. It offers the special advantage that hollow bars cut to any desired length can be detachably connected to one another without any subsequent processing in a very simple manner and rapidly. The connectors provided in this frame have expanding means, which comprises two wedges mounted displaceably in a housing. These wedges are pushed against the ends of the connector and away from one another by rotating a rotary part arranged between them, and the foot end and the head end of the connector are maintained expanded as a result. The wedges and the rotary part have a relatively complicated design, and they require a relatively great distance between the foot end and the head end.